An example of known displacement sensors of the above-described type, including a coil and a movable magnetic core, is disclosed in Patent Literature 1. Patent Literature 1 discloses applying an output voltage of the displacement sensor to a ramp forming circuit, or low-pass filter, for the purpose of suppressing needle-shaped interfering pulses in the output voltage prior to rectifying the output voltage.    Patent Literature 1: JP 2005-521048